1. Field of the Invention
The present invention relates to a light-emitting device, an electronic device, and a lighting device utilizing organic electroluminescence (EL).
2. Description of the Related Art
A light-emitting element using an organic compound as a light-emitting body, which has characteristics such as feasibility of being thinner and lighter, high speed response to input signals, and capability of direct current low voltage driving, has been expected to be applied to next-generation flat panel displays or lighting devices. In particular, a display device in which light-emitting elements are arranged in a matrix is considered to have advantages of a wide viewing angle and excellent visibility over a conventional liquid crystal display device.
The emission mechanism of a light-emitting element (organic EL element) using an organic compound as a light-emitting body is as follows. First, when voltage is applied between a pair of electrodes with a layer (EL layer) containing a light-emitting organic compound provided therebetween, electrons injected from a cathode and holes injected from an anode are transported to the EL layer, so that current flows. Then, the injected electrons and holes bring the light-emitting organic compound contained in the EL layer into an excited state, so that light is emitted from the excited light-emitting organic compound. Singlet excitation and triplet excitation are known as excited states, and light emission can probably be achieved through either of the excited states.
An EL layer included in a light-emitting element includes at least a light-emitting layer. In addition, the EL layer can have a stacked-layer structure including a hole-injection layer, a hole-transport layer, an electron-transport layer, an electron-injection layer, and/or the like, in addition to the light-emitting layer.
In the case of manufacturing a device for displaying full-color images, it is necessary to arrange light-emitting elements which emit light of at least three colors of red, green, and blue in a matrix. Examples of methods for obtaining such a structure include a method in which necessary portions of EL layers are separately colored so that light-emitting elements emitting light of different colors are provided (hereinafter such a method is referred to as a separate coloring method), a method in which each color is obtained by formation of light-emitting elements all of which emit white light and transmission of the white light through respective color filters (hereinafter such a method is referred to as a color filter method), and a method in which each color is obtained by formation of light-emitting elements all of which emit blue light or light having a shorter wavelength than blue light and transmission of the blue light or light having the shorter wavelength than blue light through respective color conversion layers (hereinafter such a method is referred to as a color conversion method). For example, Patent Document 1 discloses an organic EL display device using a color filter method.